1. Field of the Invention
The present invention relates to a fan device in which a motor rotates an impeller to generate an air flow so as to blow the air.
2. Description of Related Art
For example, electronic devices equipped with electronic components, such as personal computers and office equipment, have small fan devices for cooling the interior of the housing thereof and the electronic components. The fan devices include axial-flow fan devices and centrifugal fan devices. In these kinds of fan devices, since physical imbalance of the rotor with respect to the rotating shaft commonly occurs, a rotational balance adjustment of the rotor is performed so that the amount of the rotational imbalance is approached to zero as much as possible. In particular, in order to improve the cooling performance in response to an increase in the amount of heat generation associated with increasing performance of electronic devices, the fan devices are required to rotate at higher speed. In this regard, the rotational imbalance during the high speed rotation causes an increase of noise, and therefore, the adjustment of the rotational balance is an essential matter.
In general, the rotational balance of the rotor is adjusted by attaching a balance weight at a position axially opposite to the position of rotational imbalance in a circumferential direction of the rotor so as to balance the rotation. As the balance weight, a metal clip to be attached to the rotor may be used (disclosed in Japanese Patent Application Laid-open No. 2008-082212). Alternatively, a claylike weight that has appropriate consistency and adhesiveness and is fixed by curing, such as balancing putty, may be used (disclosed in Japanese Patent Applications Laid-open Nos. 2010-025087 and 2001-298925).
In the case of using a balancing putty, recesses (disclosed in Japanese Patent Application Laid-open No. 2010-025087) or grooves (disclosed in Japanese Patent Application Laid-open No. 2001-298925) may be formed on an end surface of a hub that forms the rotor. Then, the recesses or the grooves are filled with a required amount of the putty and the rotational balance is thereby adjusted. For example, a recess 80 with an approximately rectangular shape as shown in FIG. 8 is formed on the end surface of the hub, and a claylike weight 70 such as putty is attached in the recess 80. As shown in FIG. 8, when the amount of the weight 70 is relatively smaller than the inner volume of the recess 80, the weight 70 is attached on the outer circumferential side of the recess 80 in a direction indicated by arrow B in FIG. 8 so as to avoid the separation and drop of the weight 70 due to centrifugal force.
In order to attach the putty-like weight 70 on the outer circumferential side of the recess 80 as described above, the following procedure is used. That is, as shown in FIG. 9A, the weight 70 is placed on an end of a spatula 90, and the spatula 90 is inserted in the recess 80 so that the weight 70 faces the outer circumferential side (left side in FIGS. 9A to 9C). Then, as shown in FIGS. 9B and 9C, the spatula 90 is pulled out from the recess 80 while being pressed against an edge on the outer circumferential side of the recess 80. Accordingly, the weight 70 is adhered to the outer circumferential side of the recess 80, from the wall surface to the bottom.
Even when the amount of the weight 70 is small, the separation and drop of the weight 70 caused by the centrifugal force working in the axial direction can be prevented if the weight 70 is adhered to the wall surface at the outer circumferential side of the recess 80 as shown in FIG. 8. However, the weight 70 also tends to separate and drop due to inertial force generated in tangential direction when the rotor is started or stopped. This problem could be solved by reducing the length of the recess 80 in the circumferential direction (direction indicated by arrow A in FIG. 8) so that the weight 70 is adhered also to side wall surfaces that are in a direction crossing the circumferential direction of the recess 80. Nevertheless, as shown in FIGS. 9A to 9C, the recess 80 must be long enough in the circumferential direction to allow the spatula 90 be inserted. Therefore, if the amount of the weight 70 is relatively small, the weight 70 will not adhere to the side wall surfaces and the separation and drop of the weight 70 may easily occur. Moreover, the weight 70 is applied in uncured state when the rotational balance of the rotor is adjusted as a part of a production process. Consequently, the weight 70 may easily separate and drop due to the inertial force that is generated when the rotor is started or stopped to rotate for inspection. Even in the case of attaching the claylike weight in the groove as disclosed in Japanese Patent Application Laid-open No. 2001-298925, there is no preventive measure with respect to the inertial force in the circumferential direction, and the weight may easily separate and drop.